Abstract: The internal strain of composite laminates during a constant stress amplitude fatigue testing process was monitored with fiber Bragg gratings (FBGs) as a fatigue indicator to reveal Young's modulus decrease of the specimen, which is a direct index of damage. It is demonstrated that FBGs can not only be embedded in composite structures to detect fatigue damage during fatigue process, but also with excellent durability compared with other sensors such as foil gauges, which is most frequently used in strain measurement. After 1 million cycles, the FBGs can still keep good sensibility. It can be concluded that it is a novel way to monitor, evaluate and give crash alert for the health state of composite structures during their whole service life with FBGs as a fatigue indicator.